aptX

aptX is an audio codec that was created in the late 1980s from research at Queen's University Belfast . The name stands for A udio P rocessing T echnology . Its job is to reduce the bit rate for broadband stereo audio.

aptX was called apt-X until it was acquired by CSR plc in 2010 . In August 2015, CSR was adopted by Qualcomm . As the owner of the aptX codec family, Qualcomm currently offers the aptX, aptX Low Latency, aptX HD and aptX Adaptive variants on its website.

Overview

		SBC	aptX	aptX LL	aptX HD	aptX Adaptive		Audio CD
						@ 276 kBit / s	@ 420 kBit / s	(only for comparison)
otherwise.	Owner ( licensor )	free (part of the A2DP profile)	Qualcomm (until August 2015: CSR , until July 2010: APT Licensing Ltd. , until March 2005: Solid State Logic )					-
	begin	?	late 1980s, 2009	2012	2016	2018		1980
	chip	-	CSR8635	CSR8670	CSR8675	?		-
Audio encoding	Sampling depth	?	16-bit	16-bit	16-bit 24-bit	24-bit		16-bit
	sampling rate	44.1 kHz 48 kHz	44.1 kHz 48 kHz	44.1 kHz 48 kHz	44.1 kHz 48 kHz	44.1 kHz 48 kHz 96 kHz		44.1 kHz
	Bit rate	345 kbps (@ 48 kHz)	325 kpbs (@ 44.1 kHz) 384 kpbs (@ 48 kHz)	352 kpbs (@ 48 kHz)	576 kpbs	276 kbps	420 kpbs	1411 kbps (@ 44.1 kHz)
	Bit rate	constant	constant	constant	constant	variable		constant
	Coding latency	?	1.8 - 2.0 ms	?	1.8 - 2.0 ms	1.4 - 2.0 ms		-
	latency	170-270 ms	≈ 120 ms	≈ 40 ms	≈ 200 ms	50 - 80 ms		-
	backwards compatible with	-	SBC	SBC, aptX	SBC, aptX	SBC, aptX, aptX HD		?
Sound quality	THD + N @ 1 kHz		−67 dB or −85 dB?	−85 dB	−80 dB or −90 dB?	−90 dB	−100 dB
	Multi-tone @ 1 kHz		−100 dB	?	−100 dB	−90 dB	−100 dB
	Multi-tone @ 10 kHz		-65 dB	?	−90 dB	−85 dB	−95 dB
	Crosstalk		−120 dB	?	−155 dB	−90 dB	−200 dB
	Signal-to-noise ratio @ 1 kHz		93 dB	93 dB	129 dB	130 dB	135 dB
	PEAQ		−0.18 or −0.08?	?	0.05 or 0.04?	−0.06	0.045
	Frequency response via bluetooth		20 Hz - 22.7 kHz	20 Hz - 22.7 kHz	20 Hz - 22.7 kHz	20 Hz - 22.7 kHz

Main source

aptX

The aptX audio codec is used for wireless audio applications via the A2DP - Bluetooth profile or the coupling between a "source device" (e.g. smartphone, tablet or laptop) and an output device (sink, e.g. a Bluetooth Stereo speakers, headsets, or headphones). The technology must be integrated in both the transmitter and the receiver in order to use the acoustic advantages of aptX audio coding over the standard subband coding (SBC) prescribed by the Bluetooth standard . Products that carry the CSR aptX logo are certified for interoperability with one another.

aptX Low Latency

AptX Low Latency offers an end-to-end latency of 32 ms via Bluetooth. This is therefore less than the recommended latency times for audio-video synchronization in television operation between +40 ms and −60 ms (audio before / after video). With this latency, interactive applications for computer games, audio signals from musical instruments, multimedia, etc. can also be handled without any problems.

aptX HD

Also known as aptX Lossless, aptX-HD has a bit rate of 576 kbit / s. It supports high-resolution audio with sample rates of up to 48 kHz and sample resolutions of up to 24 bits. The "almost lossless" coding ensures high-resolution audio quality in the frequency range between 20 Hz and 20 kHz and a dynamic range of at least 120 dB. The main competitor is the LDAC codec developed by Sony.

aptX Adaptive

The aim of aptX Adaptive is to ensure that the codec automatically adapts itself in such a way that it offers optimal audio quality or latency, depending on what content is being played on the device, while at the same time taking the external RF environment into account to increase robustness. It's designed to just work with no synchronization issues for games, A / V and multimedia applications. Adaptive is backwards compatible with aptX and aptX HD, offers a compression factor between 1: 5 and 1:10 and the audio format 24-bit / 48 kHz with data rates of 276 kBit / s and 420 kBit / s.

Web links

Qualcomm aptX information ; accessed on September 23, 2018.
The aptX audio codec - Bluetooth add-on for audiophiles? - Testventure.de

Individual evidence

↑ Solid State Logic Sells APT (Audio Processing Technology) . May 12, 2005.

↑ ^a ^b ^c History of aptX : Sennheiser launched the first ever Bluetooth headset with aptX.

↑ Rayson BTM-770G : One of the first products with Qualcomm Chip CSR8670 and aptX LL

↑ Send and receive audio via Bluetooth

↑ ^a ^b Qualcomm support : The aptX Classic codec delivers “CD Like” quality and latency around 120ms. AptX Low Latency delivers “CD Like” quality as latency of ~ 40ms. The aptX HD codec delivers audio “indistinguishable from Hi Res” and a latency of around 200ms.

↑ ^a ^b ^c ^d ^e ^f aptX Adaptive product brief with comparison table (linked pdf)
↑ ^a ^b aptX by Qualcomm
↑ ^a ^b aptX HD by Qualcomm

[mixonline.com-1] Solid State Logic Sells APT (Audio Processing Technology) . May 12, 2005.

[Qualcomm_history-2] History of aptX : Sennheiser launched the first ever Bluetooth headset with aptX.

[3] Rayson BTM-770G : One of the first products with Qualcomm Chip CSR8670 and aptX LL

[4] Send and receive audio via Bluetooth

[Qualcomm-Support-5] Qualcomm support : The aptX Classic codec delivers “CD Like” quality and latency around 120ms. AptX Low Latency delivers “CD Like” quality as latency of ~ 40ms. The aptX HD codec delivers audio “indistinguishable from Hi Res” and a latency of around 200ms.